ssh into the box

ssh 192.168.1.1 -lroot

download image

cd /tmp
wget http://downloads.lede-project.org/releases/17.01.2/targets/ar71xx/generic/lede-17.01.2-ar71xx-generic-wzr-hp-g300nh-squashfs-sysupgrade.bin

upgrade

sysupgrade -c image.bin

sysupgrade -v image.bin

apt install net-tools

ifconfig eth0 192.168.11.2
arp -s 192.168.11.1 02:aa:bb:cc:dd:1a

curl -T openwrt-19.07.4-ar71xx-generic-wzr-hp-g300nh-squashfs-tftp.bin tftp://192.168.11.1

reset all settings:

mount_root
mtd -r erase rootfs_data
reboot -f

specific config:

rm /etc/config/whatever
config_generate